实例阐述浮点数解包运算过程

来源：互联网发布：佛山正大数据恢复中心编辑：程序博客网时间：2024/05/17 02:49

本文来自瑞仙的Erlang开发博客，转载请注明出处。

原文链接：http://blog.csdn.net/zhongruixian/article/details/21294855

浮点数在计算机中存储或传输时，常会遇到读出来的浮点数有N（N>10）位小数的问题，这里以Erlang实例阐述产生这种现象的原因。

浮点数的实现及其表现，详见：http://blog.csdn.net/zhongruixian/article/details/21292593

Erlang源码：

f(N) ->    Bin = <<N:32/float>>,    <<S:1, E:8, M:23>> = Bin,    io:format("~n"),    io:format("*---*----------*-------------------------*~n"),    io:format("* s * eeeeeeee * mmmmmmmmmmmmmmmmmmmmmmm *~n"),    io:format("*---*----------*-------------------------*~n"),    io:format("* ~1.2.0B * ~8.2.0B * ~23.2.0B * ~n", [S, E, M]),    io:format("*---*----------*-------------------------*~n"),    io:format("~n"),    E1 = E - 127,    M1 = calc_m(lists:flatten(io_lib:format("~23.2.0B", [M]))),    io:format("~n"),    io:format("S = s = ~w~n", [S]),    io:format("E = eeeeeeee - 127 = ~w - 127 = ~w~n", [E, E1]),    io:format("M = ~w~n", [M1]),    %% 计算公式：V=(-1)^S*2^E*M    V = math:pow(-1, S) * math:pow(2, E1) * M1,    io:format("V = (-1)^S*2^E*M = (-1)^~w*2^~w*~w = ~w~n", [S, E1, M1, V]),    io:format("~n"),    io:format("~ts ~w ~ts~w~n", [iolist_to_binary("浮点数"), N, iolist_to_binary("以[单精度]存储后根据公式（V=(-1)^S*2^E*M）运算出来的值为："), V]),    <<N1:32/float>> = Bin,    io:format("~ts ~w ~ts~w~n", [iolist_to_binary("浮点数"), N, iolist_to_binary("以[单精度]存储后                    Erlang解包出来的值为："), N1]),    io:format("~n"),    f2(N).f2(N) ->    io:format("~ts~n", [iolist_to_binary("双精度：")]),    Bin = <<N:64/float>>,    <<S:1, E:11, M:52>> = Bin,    io:format("~ns,eeeeeeeeeee,mmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmm~n"),    io:format("~1.2.0B,", [S]),    io:format("~11.2.0B,", [E]),    io:format("~52.2.0B,", [M]),    io:format("~n"),    <<N1:64/float>> = Bin,    io:format("~ts ~w ~ts~w", [iolist_to_binary("浮点数"), N, iolist_to_binary("以[双精度]存储后再读取出来的值为："), N1]),    io:format("~n"),    ok.calc_m(M) ->    calc_m(M, -1, 0).calc_m([], _E, Rt) ->    Rt1 = Rt + 1,    io:format("        M = ~w~n", [Rt]),    io:format("    1 + M = ~w~n", [Rt1]),    Rt1;calc_m([M | T], E, Rt) ->    M1 = case M of        49 -> 1;        48 -> 0    end,    V = M1 * math:pow(2, E),    io:format("~w * 2^~3w = ~w~n", [M1, E, V]),    calc_m(T, E - 1, Rt + V).

运行实例：

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